Conventional electrical discharge machining apparatuses have been disclosed that create an electrical discharge in a small gap between a workpiece and an electrode to machine the workpiece, which is immersed in a machining liquid retained in a machining tank. Such conventional electrical discharge machining apparatuses include a surface plate on which the workpiece is placed, the machining tank that surrounds the surface plate, retains the machining liquid, and has at least a part that serves as a vertically moveable ascent/descent machining tank, the ascent/descent machining tank having an outlet in its ascent/descent inner wall, the outlet allowing the machining liquid to overflow to the ascent/descent machining tank, an ascent/descent device that raises and lowers the ascent/descent machining tank, a sub-tank that receives the machining liquid that leaks out from the machining tank, and a seal arranged in a gap between the ascent/descent machining tank and the inner wall of the sub-tank to prevent the machining liquid in the machining tank from leaking out into the sub-tank (for example, see Patent Literatures 1 and 2).